Doing my first DDR2 layout and I'm hitting some conflicting requirements.
I have dogbones to an internal ground-referenced layer, and then short top layer traces at the other end going from the other via to the DDR2 pins.
I my second data lane (DQ15-8,DQS1, DM1) is looking really good except for two of the data lines I can't seem to figure out how to keep the top trace on the DDR2 side <2mm. I have to make it longer to allow the other traces to pass through with the proper spacing.
So my question is: How much of this data lane do I need to keep on the same layer? The bottom layer is reference a different ground plane (same ground but different plane), so could I put those traces there because they are all referencing a ground plane?
Picture attached. Length matching hasn't been done yet.